It has long been recognized that a syringe employed for withdrawing a liquid from an ampule or the like and ejecting such liquid into a medical solution such as an intravenous solution may also inject contaminants into the solution which may then be introduced into the blood stream of a person. At least as early as 1920 there was proposed in U.S. Pat. No. 1,363,128 an improvement in "Injection syringe" for the purpose of eliminating or at least minimizing the danger of drawing a contaminant into a human body so as to guard against "suppuration or any other detrimental effect." This problem has, however, persisted and more modern solutions thereof may be found in recently issued patents such as U.S. Pat. Nos. 3,736,932 and 3,938,513, for example. These latter devices and those of similar kind employ movable needle mounting, for example, or particularly constituted or configured filters which limit their widespread applicability.
There exists a need for a very simple and inexpensive unit for filtering all fluids expelled from an injection syringe, so as to positively preclude ejection of filterable contaminants therefrom. Furthermore, such a unit should require no separate operation or manipulation for the human persons employing syringes in filling and ejecting fluids therefrom may otherwise fail to employ the safeguard so that no practical advantage results therefrom.
The present invention provides a remarkably practicable solution to the problems identified above, and may be employed even by untrained personnel to produce truly superior protection of the person being administered a fluid from a syringe unit including the present invention.